feat: 보상 재시도 + TX 확정 대기 + 에러 포맷 통일 + 품질 고도화

- 보상 지급 실패 시 즉시 재시도(3회 backoff) + DB 기록 + 백그라운드 워커 재시도
- WaitForTx 폴링으로 블록체인 TX 확정 대기, SendTxAndWait 편의 메서드
- chain 트랜잭션 코드 중복 제거 (userTx/operatorTx 헬퍼, 50% 감소)
- AppError 기반 에러 응답 포맷 통일 (8개 코드, 전 핸들러 마이그레이션)
- TX 에러 분류 + 한국어 사용자 메시지 매핑 (11가지 패턴)
- player 서비스 테스트 20개 + chain WaitForTx 테스트 10개 추가

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/chain/client.go

@@ -147,3 +147,80 @@ func (c *Client) SendTx(tx any) (*SendTxResult, error) {
 	err := c.Call("sendTx", tx, &result)
 	return &result, err
 }
+
+// TxStatusResult mirrors the indexer.TxResult from the TOL Chain node.
+type TxStatusResult struct {
+	TxID        string `json:"tx_id"`
+	BlockHeight int64  `json:"block_height"`
+	Success     bool   `json:"success"`
+	Error       string `json:"error"`
+}
+
+// GetTxStatus queries the execution result of a transaction.
+// Returns nil result (no error) if the transaction has not been included in a block yet.
+func (c *Client) GetTxStatus(txID string) (*TxStatusResult, error) {
+	var result *TxStatusResult
+	err := c.Call("getTxStatus", map[string]string{"tx_id": txID}, &result)
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+// TxError is returned when a transaction was included in a block but execution failed.
+type TxError struct {
+	TxID    string
+	Message string
+}
+
+func (e *TxError) Error() string {
+	return fmt.Sprintf("transaction %s failed: %s", e.TxID, e.Message)
+}
+
+// DefaultTxTimeout is the default timeout for WaitForTx. PoA block intervals
+// are typically a few seconds, so 15s provides ample margin.
+const DefaultTxTimeout = 15 * time.Second
+
+// SendTxAndWait sends a transaction and waits for block confirmation.
+// It combines SendTx + WaitForTx for the common fire-and-confirm pattern.
+func (c *Client) SendTxAndWait(tx any, timeout time.Duration) (*TxStatusResult, error) {
+	sendResult, err := c.SendTx(tx)
+	if err != nil {
+		return nil, fmt.Errorf("send tx: %w", err)
+	}
+	return c.WaitForTx(sendResult.TxID, timeout)
+}
+
+// WaitForTx polls getTxStatus until the transaction is included in a block or
+// the timeout is reached. It returns the confirmed TxStatusResult on success,
+// a TxError if the transaction executed but failed, or a timeout error.
+func (c *Client) WaitForTx(txID string, timeout time.Duration) (*TxStatusResult, error) {
+	deadline := time.Now().Add(timeout)
+	interval := 200 * time.Millisecond
+
+	for {
+		result, err := c.GetTxStatus(txID)
+		if err != nil {
+			return nil, fmt.Errorf("getTxStatus: %w", err)
+		}
+		if result != nil {
+			if !result.Success {
+				return result, &TxError{TxID: txID, Message: result.Error}
+			}
+			return result, nil
+		}
+
+		if time.Now().After(deadline) {
+			return nil, fmt.Errorf("transaction %s not confirmed within %s", txID, timeout)
+		}
+
+		time.Sleep(interval)
+		// Increase interval up to 1s to reduce polling pressure.
+		if interval < time.Second {
+			interval = interval * 3 / 2
+			if interval > time.Second {
+				interval = time.Second
+			}
+		}
+	}
+}